The present invention relates to a method for inhibiting stress corrosion cracking occurring on steam generator tubes in the secondary side of nuclear power plants (NPPs) and an inhibitor therefor.
It was reported that Ni alloys, especially, ones used as steam generator tubes in nuclear power plants, frequently suffered from intergranular corrosion and stress corrosion cracking in the environment. The intergranular corrosion and stress corrosion cracking occurring on steam generator tubes in NPPs may result in the leakage of the primary cooling water into the secondary side, unexpected stop of operating NPPs, and high cost for inspecting and repairing the cracked tubes. Therefore, an inhibitor for the intergranular corrosion and stress corrosion cracking occurring on steam generator tubes in NPPs is urgently demanded.
Up to now, boric acid has been used as an inhibitor for stress corrosion cracking. However, it was proved not to be an effective inhibitor in inhibiting the intergranular corrosion and stress corrosion cracking on steam generator tubes in NPPs.
Recently, titanium oxide as an inhibitor, which introduces into the high temperature and high alkali feed water so as to inhibit stress corrosion cracking, was reported. However, quantitative analysis of its effectiveness in inhibiting the intergranular corrosion and stress corrosion cracking has not been performed yet.
Furthermore, an inhibitor or a method for inhibiting stress corrosion cracking occurring on steam generator tubes in environments contaminated with at least one lead compound such as lead oxide, lead chloride, lead sulfide which were known to accelerate stress corrosion cracking has not been developed yet.
Leading to the present invention, the intensive and thorough research on an inhibitor or a method for inhibiting stress corrosion cracking occurring on steam generator tubes in the secondary side of NPPs carried out by the present inventors aiming to avoid the problems encountered in the prior arts, and resulted in the finding that the powerful inhibition of intergranular corrosion and stress corrosion cracking occurring on steam generator tubes, compared with no inhibitor or the conventional inhibitors such as boric acid and titanium oxide, can be achieved by supplying the cerium boride as an inhibitor into the secondary side feed water of NPPs.
Therefore, it is an object of the present invention to provide a novel inhibitor in order to overcome the problems caused by the intergranular corrosion and stress corrosion cracking occurring on steam generator tubes in the secondary side of the NPPs.
It is another object of the present invention to provide cerium boride as an inhibitor for intergranular corrosion and stress corrosion cracking occurring on steam generator tubes in the secondary side of the NPPs.
And, it is a further object of the present invention to provide a method for inhibiting the intergranular corrosion and stress corrosion cracking occurring on steam generator tubes in the secondary side of NPPs, which comprises supplying the cerium boride as an inhibitor into the secondary feed water to form chromium-enriched oxide film on the surface of steam generator tubes.